Silicon carbide single crystal and method and apparatus for producing the same

ABSTRACT

A method of producing a silicon carbide single crystal in which a sublimation raw material  40  is accommodated at the side of vessel body  12  in a graphite crucible  10 , placing a seed crystal of a silicon carbide single crystal at the side of cover body  11  of the graphite crucible  10 , the sublimation raw material  40  is sublimated by a first induction heating coil  21  placed at the side of sublimation raw material  40 , a re-crystallization atmosphere is form by a second induction heating coil  20  placed at the side of cover body  11  so that the sublimation raw material  40  sublimated by the first induction heating coil  21  is re-crystallizable only in the vicinity of the seed crystal of a silicon carbide single crystal, and the sublimation raw material  40  is re-crystallized on the seed crystal of a silicon carbide single crystal, and a silicon carbide single crystal  60  is grown while keeping the whole surface of its growth surface in convex shape through the all growth processes. A high quality silicon carbide single crystal with large diameter excellent in dielectric breakdown property, heat resistance, radiation resistance and the like, suitable for electronic and optical devices and the like, and showing no contamination of polycrystals and polymorphs, no defect of micropipes and the like can be produced efficiently without cracking and the like.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a silicon carbide single crystalparticularly suitable as an electronic device, optical device or thelike, and a method and an apparatus which can produce this siliconcarbide single crystal efficiently.

2. Description of the Related Art

Silicon carbide shows a larger band gap and is excellent in dielectricbreakdown property, heat resistance, radiation resistance and the likeas compared with silicon. Therefore, silicon carbide has been noticed asan electronic device material for small-size high output semiconductorsand the like, or as an optical device material owing to its excellentoptical property. Of such silicon carbide crystals, silicon carbidesingle crystals have a merit that, when applied to devices such as awafer and the like, uniformity of properties in a wafer is particularlyexcellent as compared with a silicon carbide polycrystals.

Though there are some conventionally suggested methods of producing theabove-mentioned silicon carbide single crystal, each of them have aproblem that the resulting silicon carbide single crystal showscontamination of a polycrystal or polymorphs and crystal defects in theform of hollow pipe (so-called, micropipe).

Then, as the method of producing a silicon carbide single crystalsolving such a problem, for example, a method employing an apparatus forgenerating a silicon carbide single crystal as shown in FIG. 8 isgenerally known. This silicon carbide single crystal productionapparatus 80 comprises a graphite crucible 10 having a vessel body 12which can accommodate a sublimation raw material 40 and having a coverbody 11 which can be attached to and detached from the vessel body 12and, when installed on the vessel body 12, can arrange a seed crystal 50of a silicon carbide single crystal at approximately the center of asurface facing the sublimation raw material 40 accommodated in thevessel body 12; a supporting rod 31 fixing the graphite crucible 10 tothe inside of a quartz tube 30; and an induction heating coil 25 placed,being wound in spiral form and at an equal interval, at a part aroundthe outer periphery of the quartz tube 30 and at which part the graphitecrucible 10 is situated. In the silicon carbide single crystalproduction apparatus 80, when the induction heating coil 25 is energizedto be heated, the sublimation raw material 40 is heated by this heat.The sublimation raw material 40 sublimates when heated to giventemperature. The sublimated raw material 40 does not re-crystallizeuntil cooled to the re-crystallization temperature. Here, an atmosphereat the side of the cover body 11 has temperature lower than that in theside of the sublimation raw material 40 and the sublimation raw material40 being sublimated can re-crystallize in this atmosphere, therefore,silicon carbide re-crystallizes on the seed crystal 50 of a siliconcarbide single crystal, and the crystal of silicon carbide grows.

Under this condition, a silicon carbide single crystal 60re-crystallizes and grows on the seed crystal 50 of a silicon carbidesingle crystal, and a silicon carbide polycrystal 70 re-crystallizes andgrows on the peripheral part of the seed crystal 50 of a silicon carbidesingle crystal. Finally, as shown in FIG. 8, a concave portion 71sinking toward the cover body 11 is shaped in the form of a ring, andthe part around this concave portion 71 through at the peripheral sideof the cover body 11 are in condition wherein extraneous substances,polycrystals and polymorphs are mixed and present in a large amount. Atthe cover body 11, the whole surface at the side facing to the inside ofthe vessel body 12 is covered by crystals of silicon carbide, and on theperipheral part of the cover body 11, a silicon carbide polycrystal 70grows contacting with the inner peripheral surface of the vessel body12. Under this condition, when cooled to room temperature, stress basedon the thermal expansion difference concentrates on the side of thesilicon carbide single crystal 60 from the side of the silicon carbidepolycrystal 70, leading to breakage such as cracking and the like on thesilicon carbide single crystal 60, as shown in FIG. 9, contamination ofpolycrystals and polymorphs or defects such as micropipes and the like,in some cases. At recentness wherein production of a silicon carbidesingle crystal of large diameter is required, this phenomenon is animportant problem which should be overcome.

That is, a high quality silicon carbide single crystal showing no suchbreakages as cracking and the like, no contamination of polycrystals andpolymorphs and having no defect such as micropipes, and a method and anapparatus which can efficiently and easily produce such a high qualitysilicon carbide single crystal with large diameter, are not providedyet, and these are needed to be provided, under the present situation.

SUMMARY OF THE INVENTION

The subject of the present invention is to solve the above-mentionedconventional various problems and to attain the following object,responding to the above-mentioned requirement.

An object of the present invention is to provide a high quality siliconcarbide single crystal excellent in dielectric breakdown property, heatresistance, radiation resistance and the like, particularly suitable forelectronic devices such as semiconductor wafers and the like and opticaldevices such as emitting diodes and the like, and having nocontamination of polycrystals and polymorphs and no defects such asmicropipes and the like, and a method and an apparatus which canefficiently and easily produce the above-mentioned high quality siliconcarbide single crystal with large diameter, under condition including nobreakages such as cracking and the like.

Means for attaining the above-mentioned object are as described below.

<1> A method of producing a silicon carbide single crystal in which asublimation raw material being sublimated is re-crystallized to grow asilicon carbide single crystal, comprising

-   -   growing the silicon carbide single crystal while maintaining the        whole growing surface in a convex shape throughout all growth        processes.

<2> The method of producing a silicon carbide single crystal accordingto <1>,

-   -   wherein a crystal of silicon carbide containing a silicon        carbide single crystal is grown approximately in a protruded        shape.

<3> The method of producing a silicon carbide single crystal accordingto <1> or <2>, comprising

-   -   growing the crystal of silicon carbide containing a silicon        carbide single crystal while maintaining the approximate        protruded shape and,    -   wherein the diameter of the crystal of silicon carbide decreases        gradually toward the sublimation raw material throughout all the        growth processes.

<4> The method of producing a silicon carbide single crystal accordingto any of <1> to <3>, further comprising

-   -   accommodating the sublimation raw material in a reaction vessel,    -   placing a seed crystal of a silicon carbide single crystal at an        end approximately facing the sublimation raw material in the        reaction vessel, and    -   conducting the growth of the crystal of silicon carbide        containing a silicon carbide single crystal only in a region        excluding a part adjacent to, a peripheral side surface part in        the reaction vessel.

<5> A method of producing a silicon carbide single crystal in which asublimation raw material being sublimated is re-crystallized to grow asilicon carbide single crystal, comprising

-   -   accommodating the sublimation raw material in a reaction vessel,    -   placing the seed crystal of a silicon carbide single crystal at        the end approximately facing the sublimation raw material in the        reaction vessel, and    -   growing the crystal of silicon carbide containing a silicon        carbide single crystal only in a region excluding the part        adjacent to the peripheral side surface part in the reaction        vessel at the end.

<6> The method of producing a silicon carbide single crystal accordingto any of <2> to <5>,

-   -   wherein the crystal of silicon carbide containing a silicon        carbide single crystal is composed only of a silicon carbide        single crystal.

<7> The method of producing a silicon carbide single crystal accordingto any of <1> to <6>, further comprising

-   -   accommodating a sublimation raw material at one end side in a        reaction vessel, and placing a seed crystal of a silicon carbide        single crystal at another end side in the reaction vessel;    -   forming a sublimation atmosphere by a first heating means placed        at the one end side so as to enable sublimation of the        sublimation raw material;    -   forming a re-crystallization atmosphere by a second heating        means placed at another end side so that the sublimation raw        material being sublimate by the first heating means is        re-crystallizable only in the vicinity of the seed crystal of a        silicon carbide single crystal, and the sublimation raw material        is re-crystallized on the seed crystal of a silicon carbide        single crystal.

<8> The method of producing a silicon carbide single crystal accordingto <7>,

-   -   wherein the temperature of the re-crystallization atmosphere is        lower than the temperature of the sublimation atmosphere by 30        to 300° C., in the reaction vessel.

<9> The method of producing a silicon carbide single crystal accordingto <7> or <8>,

-   -   wherein the first heating means and the second heating means are        an induction-heatable coil.

<10> The method of producing a silicon carbide single crystal accordingto <9>,

-   -   wherein the current value of the induction heating current in        the first heating means is larger than the current value of the        induction heating current in the second heating means.

<11> The method of producing a silicon carbide single crystal accordingto <9> or <10>,

-   -   wherein the current value of the induction heating current in        the second heating means is decreased continuously or gradually        with the increase of the diameter of a growing silicon carbide        single crystal.

<12> The method of producing a silicon carbide single crystal accordingto any of <7> to <11>,

-   -   wherein if the temperature at one end side accommodating a        sublimation raw material is represented by T₁ and the        temperature at another end side at which a seed crystal of a        silicon carbide single crystal is placed is represented by T₂,        in the reaction vessel, and the temperature of the part adjacent        to the inner peripheral side surface part of the reaction vessel        at said another end side is represented by T₃, then, T₃-T₂ and        T₁-T₂ increase continuously or gradually.

<13> The method of producing a silicon carbide single crystal accordingto any of <9> to <12>,

-   -   wherein an interference preventing means capable of flowing the        induction current and preventing interference between the first        heating means and the second heating means by flowing the        induction current is placed between the first heating means and        the second heating means.

<14> The method of producing a silicon carbide single crystal accordingto <13>, wherein the interference preventing means is a coil throughwhich cooling water can flow.

<15> The method of producing a silicon carbide single crystal accordingto any of <7> to <14>, wherein the one end is a lower end and anotherend is an upper end.

<16> The method of producing a silicon carbide single crystal accordingto any of <7> to <15>, wherein the reaction vessel is a crucible placedin a quartz tube.

<17> The method of producing a silicon carbide single crystal accordingto any of <7> to <16>,

-   -   wherein a first region in which a silicon carbide single crystal        is grown and a second region situated at the outer periphery of        the first region and adjacent to the inner peripheral side        surface part of the reaction vessel, at another end, are formed        from different members, and one end of the member forming the        first region in which a silicon carbide single crystal is grown        is exposed to the inside of the reaction vessel and another end        thereof is exposed to the outside of the reaction vessel.

<18> The method of producing a silicon carbide single crystal accordingto any of <5> to <17>, wherein the surface of the part adjacent to theperipheral side surface part in the reaction vessel at another end ismade of glassy carbon.

<19> The method of producing a silicon carbide single crystal accordingto any of <1> to <18>, wherein the sublimation raw material is a siliconcarbide powder obtained by

-   -   using as a silicon source at least one compound selected from        high purity alkoxysilanes and alkoxysilane polymers, as a carbon        source a high purity organic compound generating carbon by        heating;    -   uniformly mixing the silicon source and the carbon source to        obtain a mixture; and    -   calcinating the resulted mixture by heating under a        non-oxidizing atmosphere.

<20> The method of producing a silicon carbide single crystal accordingto any of <1> to <18>, wherein the sublimation raw material is a siliconcarbide powder obtained by

-   -   using as a silicon source a high purity alkoxysilane, as a        carbon source a high purity organic compound generating carbon        by heating;    -   uniformly mixing the silicon source and the carbon source to        obtain a mixture; and    -   calcinating the resulted mixture by heating under a        non-oxidizing atmosphere.

<21> The method of producing a silicon carbide single crystal accordingto any of <1> to <18>, wherein the sublimation raw material is a siliconcarbide powder obtained by

-   -   using as a silicon source at least one of a high purity        alkoxysilane and a polymer of a high purity alkoxysilane, as a        carbon source a high purity organic compound generating carbon        by heating;    -   uniformly mixing the silicon source and the carbon source to        obtain a mixture; and    -   calcinating the resulted mixture by heating under a        non-oxidizing atmosphere.

<22> The method of producing a silicon carbide single crystal accordingto any of <1> to <18>, wherein the sublimation raw material is a siliconcarbide powder obtained by

-   -   using as a silicon source at least one compound selected from        the group consisting of high purity methoxysilane, high purity        ethoxysilane, high purity propoxysilane and high purity        butoxysilane, as a carbon source a high purity organic compound        generating carbon by heating;    -   uniformly mixing the silicon source and the carbon source to        obtain a mixture; and    -   calcinating the resulted mixture by heating under a        non-oxidizing atmosphere.

<23> The method of producing a silicon carbide single crystal accordingto any of <1> to <18>, wherein the sublimation raw material is a siliconcarbide powder obtained by

-   -   using as a silicon source at least one compound selected from        the group consisting of high purity methoxysilane, high purity        ethoxysilane, high purity propoxysilane and high purity        butoxysilane, and a polymer of them having a polymerization        degree of 2 to 15, as a carbon source a high purity organic        compound generating carbon by heating;    -   uniformly mixing the silicon source and the carbon source to        obtain a mixture, and calcinating the resulted mixture by        heating under a non-oxidizing atmosphere.

<24> The method of producing a silicon carbide single crystal accordingto any of <1> to <18>, wherein the sublimation raw material is a siliconcarbide powder obtained by

-   -   using as a silicon source at least one of compound selected from        the group consisting of high purity monoalkoxysilanes, high        purity dialkoxysilanes, high purity trialkoxysilanes and high        purity tetraalkoxysilanes, and a polymer of them having a        polymerization degree of 2 to 15, as a carbon source a high        purity organic compound generating carbon by heating;    -   uniformly mixing the silicon source and the carbon source to        obtain a mixture; and    -   calcinating the resulted mixture by heating under a        non-oxidizing atmosphere.

<25> The method of producing a silicon carbide single crystal accordingto any of <19> to <24>, wherein the silicon source is atetraalkoxysilane polymer and the carbon source is a phenol resin.

<26> The method of producing a silicon carbide single crystal accordingto any of <19> to <25>, wherein each content of impurity elements in thesilicon carbide powder is 0.5 ppm or less.

<27> A silicon carbide single crystal produced by the method ofproducing a silicon carbide single crystal according to any of <1> to<26>.

<28> The silicon carbide single crystal according to <27>, wherein thecrystal defect in the form of hollow pipe of which image is opticallydetected is 100/cm² or less.

<29> The silicon carbide single crystal according to <27> or <28>,wherein the total content of impurity elements is 10 ppm or less.

<30> An apparatus for generating a silicon carbide single crystal inwhich a sublimation raw material being sublimated is re-crystallized togrow a silicon carbide single crystal, comprising

-   -   a crucible provided with a vessel body to accommodate a        sublimation raw material and a cover body attachable to and        detachable from the vessel body and, when the cover body is        installed on the vessel body, a seed crystal of a silicon        carbide single crystal can be arranged at a surface facing the        inside of the vessel body;    -   a first induction heating coil placed in the state wound around        the outer periphery of a part or the crucible when the        sublimation raw material is accommodated, and forming a        sublimation atmosphere so as to enable sublimation of the        sublimation raw material; and    -   a second induction heating coil placed in the state wound around        the outer periphery of a part of a crucible where the seed        crystal is placed, forming a re-crystallization atmosphere so        that the sublimation raw material being sublimate by the first        induction heating coil is re-crystallizable only in the vicinity        of the seed crystal of a silicon carbide single crystal, and        re-crystallizing the sublimation raw material on the seed        crystal of a silicon carbide single crystal.

The above-described method of producing a silicon carbide single crystaldescribed in <1> is a method in which a sublimation raw material beingsublimated is re-crystallized to grow a silicon carbide single crystal,wherein the above-mentioned silicon carbide single crystal is grownwhile maintaining the whole growing surface in a convex shape throughoutthe all growth processes. In this method of producing a silicon carbidesingle crystal, the above-mentioned concave portion sunk toward thereverse direction to the growth direction is not shaped in the form ofring at the whole surface of the growth surface of the growing siliconcarbide single crystal. Therefore, a high quality silicon carbide singlecrystal is produced having no conventional various problems describedabove, namely, showing no breakages such as cracking and the like andhaving no contamination of polycrystals and polymorphs and no crystaldefects present such as micropipes and the like.

In the above-mentioned methods of generating a silicon carbide singlecrystal described in <2> and <3>, a crystal of silicon carbidecontaining a silicon carbide single crystal is grown approximately inshape in <1>, consequently, the above-mentioned concave portion sunktoward the reverse direction to its growth direction is not present atall, in the growing silicon carbide single crystal. Therefore, a highquality silicon carbide single crystal is produced having noconventional various problems described above, namely, showing nobreakages such as cracking and the like and having no contamination ofpolycrystals and polymorphs and no crystal defects present such asmicropipes and the like.

In the above-mentioned method of producing a silicon carbide singlecrystal described in <4>, the above-mentioned sublimation raw materialis accommodated in a reaction vessel, placing a seed crystal of asilicon carbide single crystal at the end approximately facing thesublimation raw material in the reaction vessel, and growth of theabove-mentioned crystal of silicon carbide containing a silicon carbidesingle crystal is conducted only in a region excluding the part adjacentto the peripheral side surface part in the reaction vessel, at theabove-mentioned end, in any of <1> to <3>. Therefore, theabove-mentioned concave portion sunk toward the reverse direction to thegrowth direction of the silicon carbide single crystal is not shaped inthe form of ring, in the growing silicon carbide single crystal,further, the silicon carbide single crystal does not grow contactingwith the peripheral surface part in the reaction vessel. Therefore,stress based on the thermal expansion difference does not concentrate onthe silicon carbide single crystal side from the silicon carbidepolycrystal side when a grown silicon carbide single crystal is cooledto room temperature, and defects such as cracking and the like do notoccur on the resulting silicon carbide single crystal. As a result, ahigh quality silicon carbide single crystal is efficiently and securelyproduced having no conventional various problems described above,namely, showing no breakages such as cracking and the like and having nocontamination of polycrystals and polymorphs and no crystal defectspresent such as micropipes and the like.

The method of producing a silicon carbide single crystal described in<5> is a method of producing a silicon carbide single crystal in which asublimation raw material being sublimated is re-crystallized to grow asilicon carbide single crystal, wherein the above-mentioned sublimationraw material is accommodated in a reaction vessel, the above-mentionedseed crystal of a silicon carbide single crystal is placed at the endapproximately facing the sublimation raw material in the reactionvessel, and the above-mentioned crystal of silicon carbide containing asilicon carbide single crystal is grown only in, a region excluding thepart adjacent to the peripheral surface part in the reaction vessel, atthe above-mentioned end. Therefore, the above-mentioned silicon carbidesingle crystal does not grow contacting with the peripheral surface partin the reaction vessel, at the above-mentioned end. Stress based onthermal expansion difference on the silicon carbide single crystal sidefrom the silicon carbide polycrystal side when a grown silicon carbidesingle crystal is cooled to room temperature, and defects such ascracking and the like do not occur on the resulting silicon carbidesingle crystal. As a result, a high quality silicon carbide singlecrystal is produced having no conventional various problems describedabove, namely, showing no breakages such as cracking and the like andhaving no crystal defects present such as contamination of polycrystalsand polymorphs and micropipes and the like.

In the method of producing a silicon carbide single crystal described in<6>, the above-mentioned crystal of silicon carbide containing a siliconcarbide single crystal is composed only of a silicon carbide singlecrystal, in any of <2> to <5>. Therefore, a silicon carbide singlecrystal having a larger diameter is obtained, and it is not necessary toseparate the silicon carbide single crystal from a silicon carbidepolycrystal and the like.

In the method of producing a silicon carbide single crystal described in<7>, the above-mentioned sublimation raw material is accommodated at oneend side in the above-mentioned reaction vessel, and the above-mentionedseed crystal of a silicon carbide single crystal is placed at anotherend side in the reaction vessel, a sublimation atmosphere is formed by afirst heating means placed at the above-mentioned one end side so as toenable sublimation of the sublimation raw material, a re-crystallizationatmosphere is formed by a second heating means placed at theabove-mentioned another end side so that the above-mentioned sublimationraw material being sublimated by the above-mentioned first heating meansis re-crystallizable only in the vicinity of the above-mentioned seedcrystal of a silicon carbide single crystal, and the sublimation rawmaterial is re-crystallized on the above-mentioned seed crystal of asilicon carbide single crystal, in any of <1> to <6>.

In this method of producing a silicon carbide single crystal, heatingfor formation of a sublimation atmosphere so as to enable sublimation ofthe above-mentioned sublimation raw material is conducted by theabove-mentioned first heating means, formation of a re-crystallizationatmosphere so as to enable re-crystallization only on theabove-mentioned seed crystal of a silicon carbide single crystal isconducted by the above-mentioned second heating means, as a result,re-crystallization can be conducted selectively only on theabove-mentioned seed crystal of a silicon carbide single crystal and thepart in the vicinity of this, and the above-mentioned silicon carbidepolycrystal does not grow contacting with the peripheral side surfacepart in the reaction vessel, at the above-mentioned end. And, stressbased on thermal expansion difference on the silicon carbide singlecrystal side from the silicon carbide polycrystal side when a grownsilicon carbide single crystal is cooled to room temperature, anddefects such as cracking and the like do not occur on the resultingsilicon carbide single crystal. As a result, a high quality siliconcarbide single crystal is produced having no conventional variousproblems described above, namely, showing no breakages such as crackingand the like and having no crystal defects present such as contaminationof polycrystals and polymorphs and micropipes and the like.

In the method of producing a silicon carbide single crystal described in<8>, the temperature of the re-crystallization atmosphere is lower thanthe temperature of the sublimation atmosphere by 30 to 300° C., in theabove-mentioned reaction vessel, in <7>.

In the method of producing a silicon carbide single crystal described in<9>, the above-mentioned first heating means and the above-mentionedsecond heating means are an induction-heatable coil, in <7> or <8>.Therefore, control of the temperature of the above-mentioned firstheating means for forming the above-mentioned sublimation atmosphere andcontrol of the temperature of the above-mentioned second heating meansfor forming the above-mentioned re-crystallization atmosphere can beconducted easily and securely, by induction heating by this coil.

In the method of producing a silicon carbide single crystal described in<10>, the current value of the induction heating current in the firstheating means is larger than the current value of the induction heatingcurrent in the second heating means, in any of <7> to <9>. Therefore,the temperature of the re-crystallization atmosphere in the vicinity ofon the above-mentioned seed crystal is maintained lower than thetemperature of the above-mentioned sublimation atmosphere, andre-crystallization is conducted easily.

In the method of producing a silicon carbide single crystal described in<11>, the current value of the induction heating current in theabove-mentioned second heating means is decreased continuously orgradually with the increase of the diameter of a growing silicon carbidesingle crystal, in any of <7> to <10>. By this constitution, the heatingquantity by the above-mentioned second heating means is controlled to besmaller with the growth of the above-mentioned silicon carbide singlecrystal, therefore, re-crystallization is conducted only in the vicinityof the above-mentioned silicon carbide single crystal keeping ongrowing, and a polycrystal is not formed around the silicon carbidesingle crystal.

In the method of producing a silicon carbide single crystal described in<12>, if the temperature at one end side accommodating a sublimation rawmaterial is represented by T₁ and the temperature at another end side atwhich a seed crystal of a silicon carbide single crystal is arranged isrepresented by T₂, in the reaction vessel, and the temperature of thepart adjacent to the inner peripheral side surface part of the reactionvessel, at another end side, is represented by T₃, then, T₃-T₂ and T₁-T₂increase continuously or gradually, in any of <7> to <11>. When T₁-T₂increases continuously or gradually, even if a silicon carbide singlecrystal keeps on growing toward the above-mentioned one end side, withthe lapse of time, the crystal growth peak side of the silicon carbidesingle crystal is always maintained at the condition susceptible tore-crystallization. On the other hand, when T₃-T₂ increases continuouslyor gradually, even if a silicon carbide single crystal keeps on growingtoward the peripheral direction at the above-mentioned another end side,with the lapse of time, the crystal growth peripheral end side of thesilicon carbide single crystal is always maintained at the conditionsusceptible to re-crystallization. As a result, production of a siliconcarbide single crystal is effectively suppressed, and the siliconcarbide single crystal keeps on growing toward a direction along whichits thickness increases and its diameter enlarges, and finally, asilicon carbide single crystal of a larger diameter is obtained undercondition without contamination of a silicon carbide polycrystal and thelike.

In the method of producing a silicon carbide single crystal described in<13>, an interference preventing means capable of flowing the inductioncurrent and preventing interference between the first heating means andthe second heating means by flowing the induction current is placedbetween the first heating means and the second heating means, in any of<9> to <12>. Owing to this constitution, when induction heating by theabove-mentioned first heating means and induction heating by theabove-mentioned second heating means are conducted simultaneously,induction current flows through the interference preventing means andthe interference preventing means minimizes and prevents interferencebetween them.

In the method of producing a silicon carbide single crystal described in<14>, the interference preventing means is a coolable coil, in <13>.Since this coil is cooled even if induction current flows in the coil toheat the coil, this coil does not heat the above-mentioned reactionvessel. Namely, control of the temperature of the above-mentionedreaction vessel is easy.

In the method of producing a silicon carbide single crystal described in<15>, the above-mentioned one end is a lower end and the above-mentionedanother end is an upper end, in any of <7> to <14>. Therefore, theabove-mentioned sublimation raw material is accommodated in the lowerportion of the above-mentioned reaction vessel, and sublimation of thesublimation raw material is conducted smoothly, and the above-mentionedsilicon carbide single crystal grows toward lower direction, namely,grows under condition without an excess load toward the gravitydirection.

In the method of producing a silicon carbide single crystal described in<16>, the reaction vessel is a crucible placed in a quartz tube, in anyof <7> to <15>. Namely, since sublimation and re-crystallization of theabove-mentioned sublimation raw material, and growth of theabove-mentioned silicon carbide single crystal are conducted in thesealed system in the quartz tube, the control of them is easy.

In the method of producing a silicon carbide single crystal described in<17>, a region in which the silicon carbide single crystal is grown anda region situated at the outer periphery of the above-mentioned regionand adjacent to the inner peripheral side surface part of theabove-mentioned reaction vessel, are formed from different members, andone end of the member forming the region in which the silicon carbidesingle crystal is grown is exposed to the inside of the reaction vesseland another end thereof is exposed to the outside of the reactionvessel, in any of <7> to <16>. Since the region in which the siliconcarbide single crystal is grown (inside region) and the region situatedat the outer periphery of the above-mentioned region and adjacent to theinner peripheral side surface part of the above-mentioned reactionvessel (outside region) are formed from different members, when heatingis conducted by the above-mentioned second heating means, theabove-mentioned outside region situated at the second heating means sideis heated easily, however, the inside region is not heated easily by thedifference of contact resistance with the outside region. Therefore,even if heating is conducted by the above-mentioned second heatingmeans, a difference in temperature occurs between the above-mentionedoutside region and the above-mentioned inside region, and since theabove-mentioned inside region is not heated easily than theabove-mentioned outside region, temperature is maintained low and theabove-mentioned re-crystallization of silicon carbide is conductedeasily. Further, since the opposite side to the inside of theabove-mentioned reaction vessel in the member forming theabove-mentioned inside region is exposed to the outside of the reactionvessel and consequently heat is easily discharged out of the reactionvessel, when heating is conducted by the above-mentioned second heatingmeans, the above-mentioned inside region is not heated easily than theabove-mentioned outside region, a difference in temperature occursbetween the above-mentioned outside region and the above-mentionedinside region, the temperature of the above-mentioned inside region ismaintained lower than the temperature of the above-mentioned outsideregion, consequently, the above-mentioned re-crystallization of siliconcarbide is conducted easily. As a result, a silicon carbide singlecrystal does not grow easily in the above-mentioned outside region, anda silicon carbide single crystal re-crystallizes and grows selectivelyonly in the inside region.

In the method of producing a silicon carbide single crystal described in<18>, the surface of the part adjacent to the inner peripheral sidesurface part of the reaction vessel is made of glassy carbon, in any of<5> to <17>. Therefore, the part adjacent to the inner peripheral sidesurface part of the reaction vessel does not easily causere-crystallization than regions other than the above-mentioned adjacentpart. As a result, a crystal of silicon carbide does not grow at theabove-mentioned adjacent part, at the above-mentioned another end, and asilicon carbide single crystal re-crystallizes and grows selectivelyonly in regions other than the above-mentioned adjacent part.

In the methods of generating a silicon carbide single crystal describedin <19> to <24>, the above-mentioned sublimation raw material is asilicon carbide powder obtained by using as a silicon source at leastone compound selected from high purity alkoxysilanes and alkoxysilanepolymers, using as a carbon source a high purity organic compoundgenerating carbon by heating, uniformly mixing the silicon source andthe carbon source to obtain a mixture, and calcinating the resultedmixture by heating under a non-oxidizing atmosphere, in any of <1> to<18>. Since the sublimation raw material is a high purity siliconcarbide powder, contamination of polycrystals and polymorphs into asilicon carbide single crystal does not occur when growing a siliconcarbide single crystal, and a silicon carbide single crystal growssmoothly and the resulted silicon carbide single crystal contains nodefects such as micropipes and the like.

In the method of producing a silicon carbide single crystal described in<25>, the above-mentioned silicon source is a tetraalkoxysilane polymerand the above-mentioned carbon source is a phenol resin, in any of <19>to <24>. Therefore, the above-mentioned sublimation raw material isobtained easily at low cost.

In the method of producing a silicon carbide single crystal described in<26>, each content of impurity elements in the above-mentioned siliconcarbide powder is 0.5 ppm or less, in any of <19> to <25>. Therefore,the above-mentioned sublimation raw material has extremely high purity,and contamination of polycrystals and polymorphs into theabove-mentioned silicon carbide single crystal and generation of crystaldefects are effectively suppressed.

The silicon carbide single crystal described in <27> is produced by themethod of producing a silicon carbide single crystal described in any of<1> to <26>. Therefore, the resulting silicon carbide single crystalshows no breakages such as cracking and the like and has no crystaldefects such as contamination of polycrystals and polymorphs andmicropipes and the like present, namely, has extremely high quality andexcellent in dielectric breakdown property, heat resistance, radiationresistance and the like and suitable particularly for electronic devicessuch as semiconductor wafers and the like, optical devices such as lightemitting diodes and the like.

In the silicon carbide single crystal described in <28>, the crystaldefects in the form of hollow pipe of which image is 100/cm² or less, in<27>. Therefore, the silicon carbide single crystal has extremely highquality, particularly excellent in dielectric breakdown property, heatresistance, radiation resistance and the like, and suitable particularlyfor electronic devices such as semiconductor wafers and the like,optical devices such as light emitting diodes and the like.

In the silicon carbide single crystal described in <29>, the totalcontent of the above-mentioned impurity elements is 10 ppm or less, in<27> or <28>. Therefore, the silicon carbide single crystal has veryhigh quality.

An apparatus for generating a silicon carbide single crystal describedin <30> is an apparatus for generating a silicon carbide single crystalwherein a sublimation raw material being sublimated is re-crystallizedto grow a silicon carbide single crystal.

This silicon carbide single crystal production apparatus comprises atleast a crucible having a vessel body and a cover body, a firstinduction heating coil and a second induction heating coil.

In the above-mentioned crucible, the above-mentioned vessel bodyaccommodates the above-mentioned sublimation raw material. Theabove-mentioned cover body can be attached to and detached from theabove-mentioned vessel body. When the cover body is installed to theabove-mentioned vessel body, placing a seed crystal of a silicon carbidesingle crystal on a surface facing the inside of the vessel body. Theabove-mentioned first induction heating coil is placed, being wound, atthe outer periphery of the part accommodating the above-mentionedsublimation raw material, in the above-mentioned crucible, and thisforms a sublimation atmosphere so as to enable sublimation of thesublimation raw material, to sublimate the sublimation raw material. Theabove-mentioned second induction heating coil is placed, being wound, atthe outer periphery of the part at which the above-mentioned seedcrystal is placed, in the above-mentioned crucible, and this forms are-crystallization atmosphere so that the above-mentioned sublimationraw material being sublimate by the above-mentioned first inductionheating coil is re-crystallizable only in the vicinity of theabove-mentioned seed crystal of a silicon carbide single crystal, andre-crystallizes the sublimation raw material on the above-mentioned seedcrystal of a silicon carbide single crystal. Owing to this constitution,a silicon carbide single crystal is grown while maintaining the wholegrowing surface in a convex shape throughout the all growth processes, aconcave portion sunk toward the reverse direction to the growthdirection is not shaped in the form of ring, further, a silicon carbidesingle crystal does not grow contacting with the peripheral side surfacepart in the vessel body. Consequently, stress based on thermal expansiondifference on the silicon carbide single crystal side from the siliconcarbide polycrystal side when a grown silicon carbide single crystal iscooled to room temperature, and defects such as cracking and the like donot occur on the resulting silicon carbide single crystal. As a result,a high quality silicon carbide single crystal is efficiently andsecurely produced showing no breakages such as cracking and the like andhaving no crystal defects present such as contamination of polycrystalsand polymorphis and micropipes and the like.

This application claims benefit of priority based on Japanese PatentApplication previously filed by this applicant, namely, No. 2000-402730(filing date Dec. 28, 2000) and No. 2001-111374 (filing date Apr. 10,2001), the specifications of which are incorporated by reference herein.

BRIEF EXPLANATION OF THE DRAWINGS

Other objects, features, and advantages of the invention will becomeapparent from the following description taken together with thedrawings, in which:

FIG. 1 is a schematic view for illustrating the initial condition in themethod of producing a silicon carbide single crystal of the presentinvention.

FIG. 2 is a schematic view for illustrating a condition in which asilicon carbide single crystal is being produced by the method ofproducing a silicon carbide single crystal of the present invention.

FIG. 3 is a schematic view of the silicon carbide single crystal of thepresent invention produced by the method of producing a silicon carbidesingle crystal of the present invention.

FIG. 4 is a schematic illustration view showing one example of thecrucible used in the method of producing a silicon carbide singlecrystal of the present invention.

FIG. 5 is a schematic illustration view showing another example of thecrucible used in the method of producing a silicon carbide singlecrystal of the present invention.

FIG. 6 is a schematic view of the silicon carbide single crystal of thepresent invention produced by the method of producing a silicon carbidesingle crystal of the present invention.

FIG. 7 is a schematic view of the silicon carbide single crystal of thepresent invention produced by the method of producing a silicon carbidesingle crystal of the present invention.

FIG. 8 is a schematic view for illustrating a condition in which asilicon carbide single crystal is being produced by a conventionalmethod of producing a silicon carbide single crystal.

FIG. 9 is a schematic view of a silicon carbide single crystal-producedby a conventional method of producing a silicon carbide single crystal.

EXPLANATION OF MARKS

-   -   1: Apparatus for generating a silicon carbide single crystal    -   10: Graphite crucible    -   11: Cover body    -   12: Vessel body    -   13: Peripheral side surface part    -   15: Inside region forming part    -   20: Second induction heating coil    -   21: First induction heating coil    -   22: Interference preventing coil    -   25: Induction heating coil    -   30: Quartz tube    -   31: Supporting rod    -   40: Sublimation raw material    -   50: Seed crystal of silicon carbide single crystal    -   60: Silicon carbide single crystal    -   70: Silicon carbide polycrystal    -   71: Concave portion    -   80: Conventional apparatus for generating a silicon carbide        single crystal

DETAILED DESCRIPTION OF THE INVENTION

(Method of Generating Silicon Carbide Single Crystal)

The method of producing a silicon carbide single crystal of the presentinvention will be described below.

The method of producing a silicon carbide single crystal of the presentinvention is a method of producing a silicon carbide single crystal inwhich a sublimation raw material being sublimated is re-crystallized ona seed crystal of a silicon carbide single crystal to grow a siliconcarbide single crystal.

In the method of producing a silicon carbide single crystal of thepresent invention, the following first to third embodiments are listed,and among them, the third embodiment is a preferable embodiment having acontent combining the first embodiment and the second embodiment.

In the first embodiment, the above-mentioned silicon carbide singlecrystal is grown while maintaining the whole growing surface in a convexshape throughout the all growth processes.

In the second embodiment, the above-mentioned sublimation raw materialis accommodated in a reaction vessel, placing a seed crystal of asilicon carbide single crystal at the end approximately facing thesublimation raw material in the reaction vessel, and the above-mentionedsilicon carbide single crystal is grown only in regions excluding thepart adjacent to the peripheral side surface part in the reactionvessel, at the above-mentioned end.

In the third embodiment, the above-mentioned sublimation raw material isaccommodated in a reaction vessel, placing a seed crystal of a siliconcarbide single crystal at the end approximately facing the sublimationraw material in the reaction vessel, and the above-mentioned siliconcarbide single crystal is grown while maintaining the whole growingsurface in a convex shape throughout the all growth processes and onlyin a regions (inside part) excluding the part (outside pate) adjacent tothe peripheral side surface part in the reaction vessel, at theabove-mentioned end.

—Reaction Vessel—

The reaction vessel is not particularly restricted and can beappropriately selected depending on its object, and it is preferablethat it can contain the above-mentioned sublimation raw material insideand it has an end on which the above-mentioned seed crystal of a siliconcarbide single crystal can be placed, at a position approximately facingthe sublimation raw material.

The form of the above-mentioned end is not particularly restricted andpreferably in the form of approximate flat, for example.

The site accommodating the above-mentioned sublimation raw material isnot particularly restricted, and preferably an end approximately facingone end at which the above-mentioned seed crystal of a silicon carbidesingle crystal can be placed. In this case, the inside of theabove-mentioned reaction vessel is in the form of cylinder, and the axisof this cylindrical form may be linear or curved, and the form of asection vertical to the axis direction of this cylindrical form may becircle or polygon. Suitably listed as the preferable example of thecircular form are those having a linear axis and having a sectionvertical to the axis direction, in the form of circle.

When two ends are present in the above-mentioned reaction vessel, theabove-mentioned sublimation raw material is accommodated in one end sideand the above-mentioned seed crystal of a silicon carbide single crystalis placed in another end side. Hereinafter, the above-mentioned one endmay be referred to as “sublimation raw material accommodating part”, andthe above-mentioned another end may be referred to as “seed crystalplacing part”.

The form of the above-mentioned one end (sublimation raw materialaccommodating part) is not particularly restricted, and may be in theflat form, or a structure for promoting soaking (for example, convexportion and the like) may be appropriately provided.

In the above-mentioned reaction vessel, it is preferable that theabove-mentioned another end (seed crystal placing part) is designed soas to enable attachment and detachment. In this case, it is advantageousin that a grown silicon carbide single crystal can be easily separatedfrom the reaction vessel only by removing another end (seed crystalplacing part).

Suitably listed such a reaction vessel is, for example, a reactionvessel comprising a vessel body which can accommodate a sublimation rawmaterial and a cover body which can be attached to and detached from thevessel body and, when installed on the vessel body, can carry a seedcrystal of a silicon carbide single crystal placed at approximately thecenter of a surface facing the above-mentioned sublimation raw materialaccommodated in the reaction vessel, and other vessels.

The positional relation between the above-mentioned one end (sublimationraw material accommodating part) and the above-mentioned another end(seed crystal placing part) is not particularly restricted and can beappropriately selected depending on its object, and it is preferablethat the above-mentioned one end (sublimation raw material accommodatingpart) is a lower end and the above-mentioned another end (seed crystalplacing part) is an upper end, namely, that the above-mentioned one end(sublimation raw material accommodating part) and the above-mentionedanother end (seed crystal placing part) are situated along the gravitydirection. This case is preferable in that sublimation of theabove-mentioned sublimation raw material is conducted smoothly, andgrowth of the above-mentioned silicon carbide single crystal isconducted toward lower direction, namely, conducted under conditionwithout an excess load toward the gravity direction.

At the above-mentioned one end (sublimation raw material accommodatingpart), a member formed of a material excellent in heat conductivity, forexample, may be placed for the purpose of conducting sublimation of theabove-mentioned sublimation raw material efficiently.

Suitably listed as this member are, for example, members in the form ofreverse cone or reverse truncated cone of which outer periphery canclosely contact with the peripheral side surface part in theabove-mentioned reaction vessel and of which inner diameter graduallyincreases when approaching the above-mentioned another end (seed crystalplacing part), and other members.

On the portion exposed to the outside of the above-mentioned reactionvessel, threading, concave portion for measuring temperature, and thelike may be provided, depending on the object, and the concave portionfor measuring temperature is preferably provided at at least one of theabove-mentioned one end side and the above-mentioned another end side.

The material of the above-mentioned reaction vessel is not particularlyrestricted and can be appropriately selected depending on the object,and it is preferable that the reaction vessel is formed of a materialexcellent in durability, heat resistance, heat conductivity and thelike, and particularly preferable is graphite in that contamination ofpolycrystals and polymorphs due to generation of impurities is littleand control of sublimation and re-crystallization of the above-mentionedsublimation raw material is easy, and the like, in addition to theabove-mentioned properties.

The above-mentioned reaction vessel may be formed from a single member,or two or more members, and members can be appropriately selecteddepending on the object. When formed from two or more members, it ispreferable that the above-mentioned another end (seed crystal placingpart) is formed from two or more members, and it is more preferable thatthe center part and its peripheral part of the above-mentioned anotherend (seed crystal placing part) are formed from different members sincethe temperature difference or temperature gradient can be formed.Specifically, it is particularly preferable in the above-mentionedreaction vessel that a region in which a silicon carbide single crystalis grown (inside region) as the center part and a region situated at theouter periphery of the above-mentioned inside region and adjacent to theinner peripheral side surface part of the reaction vessel (outsideregion) as the peripheral part are formed from different members, andone end of a member forming the inside region is exposed to the insideof the reaction vessel and another end thereof is exposed to the outsideof the reaction vessel.

In this case, when the above-mentioned another end (seed crystal placingpart) is heated from its outside, the above-mentioned outside region isheated easily, however, the above-mentioned inside region is not easilyheated due to contact resistance with the outside region. Therefore, adifference in temperature occurs between the above-mentioned outsideregion and the above-mentioned inside region, the temperature of theinside region is maintained slightly lower than the temperature of theoutside region, and silicon carbide can be re-crystallized more easilyin the inside region than in the outside region. Further, since theabove-mentioned another end of a member forming the above-mentionedinside region is exposed to the outside of the above-mentioned reactionvessel, the inside region easily discharges heat to the outside of theabove-mentioned reaction vessel, consequently, silicon carbide isre-crystallized more easily in the inside region than in the outsideregion.

Here, the embodiment in which the above-mentioned another end of amember forming the above-mentioned inside region is exposed to theoutside of the above-mentioned reaction vessel is not particularlyrestricted, and shapes having the inside region as the bottom surfaceand having a diameter varying (increasing or decreasing) continuously ordiscontinuously toward the outside of the above-mentioned reactionvessel, and the like are listed.

Specifically listed as such a form are pillar forms having the insideregion as the bottom surface (cylinder, prism and the like are listed,and cylinder is preferable), truncated pyramidal forms (truncated cone,truncated pyramid, reverse truncated cone, reverse truncated pyramid andthe like are listed, and reverse truncated cone is preferable), and thelike.

It is preferable in the above-mentioned reaction vessel that the surfaceof a region (outside region) situated at the outer periphery of theabove-mentioned region (inside region) in which a silicon carbide singlecrystal is grown and adjacent to the inner peripheral side surface partof the reaction vessel, at the above-mentioned another end (seed crystalplacing part), is made of glassy carbon or amorphous carbon. In thiscase, the above-mentioned outside region is preferable in thatre-crystallization does not occur easily as compared with theabove-mentioned inside region.

It is preferable that the above-mentioned reaction vessel is surroundedby a heat insulating material and the like. In this case, it ispreferable that the above-mentioned heat insulating material and thelike are not provided at approximately the center of the above-mentionedone end (sublimation raw material accommodating part) and theabove-mentioned another end (seed crystal placing part) in theabove-mentioned reaction vessel, for the purpose of forming atemperature measuring window. When the above-mentioned temperaturemeasuring window is provided at approximately the center of theabove-mentioned one end (sublimation raw material accommodating part),it is preferable that a graphite cover member and the like are furtherprovided for preventing falling the above-mentioned heat insulatingmaterial powder and the like.

It is preferable that the above-mentioned reaction vessel is placed in aquartz tube. This is preferable in that loss of heat energy forsublimation and re-crystallization of the above-mentioned sublimationraw material is small.

A high purity quartz tube is available, and use of the high purityproduct is advantageous in that contamination of metal impurities issmall.

—Sublimation Raw Material—

Regarding the above-mentioned sublimation raw material, the polymorphsof a crystal, use amount, purity, its production method and the like arenot particularly restricted as long as the material is made of siliconcarbide, and can be appropriately selected depending on the object.

As the polymorphs of a crystal of the above-mentioned sublimation rawmaterial, for example, 4H, 6H, 15R, 3C and the like listed, and amongthem, 6H and the like are suitably listed. These are preferably usedalone, however, two or more of them may be used in combination.

The use amount of the above-mentioned sublimation raw material can beappropriately selected depending on the size of a silicon carbide singlecrystal produced, the size of the above-mentioned reaction vessel, andthe like.

The purity of the above-mentioned sublimation raw material is preferablyhigher from the standpoint of preventing contamination of polycrystalsand polymorphs into a silicon carbide single crystal produced as much aspossible, and specifically, it is preferable that the content of eachimpurity element is 0.5 ppm or less.

Here, the content of the above-mentioned impurity elements is impuritycontent by chemical analysis, and only means a reference values, andpractically, evaluation differs depending on whether the above-mentionedimpurity elements are uniformly distributed in the above-mentionedsilicon carbide single crystal or not, or whether they are localized ornot. Here, “impurity element” means elements belonging to Groups I toXVII in the Periodic Table according to 1989, IUPAC Inorganic ChemicalNomenclature Revision and at the same time having an atomic number of 3or more (excluding carbon atom, oxygen atom and silicon atom). Whendopant elements such as nitrogen, aluminum and the like are added byintention for imparting n-type or p-type conductivity to a siliconcarbide single crystal to be grown, these elements are also excluded.

A silicon carbide powder as the above-mentioned sublimation raw materialis obtained, for example, by dissolving at least one silicon compound asa silicon source, at least one organic compound generating carbon byheating as a carbon source, and a polymerization catalyst orcross-linking catalyst in a solvent and drying the resulted solution togive a powder, and calcinating the resulted powder under a non-oxidaingatmosphere.

As the above-mentioned silicon compound, liquid compounds and solidcompounds can be used together, however, at least one compound isselected from liquid compounds.

As the above-mentioned liquid compound, alkoxysilanes and alkoxysilanepolymers are suitably used.

As the above-mentioned alkoxysilane, for example, methoxysilane,ethoxysilane, propoxysilane, butoxysilane and the like are listed, andamong them, ethoxysilane is preferable from the standpoint of handling.

The above-mentioned alkoxysilane may be any of monoalkoxysilanes,dialkoxysilane, trialkoxysilane and tetraalkoxysilane, andtetraalkoxysilanes are preferable.

As the above-mentioned alkoxysilane polymer, lower molecular weightpolymers (oligomers) having a degree of polymerization of from about 2to 15 and silicic acid polymers are listed. For example, atetraethoxysilane oligomer is mentioned.

As the above-mentioned solid compound, silicon oxides such as SiO,silica sol (colloidal ultrafine silica-containing liquid, having an OHgroup and alkoxyl group inside), silicon dioxides (silica gel, finesilica, quartz powder) and the like are listed.

The above-mentioned silicon compounds may be used alone or incombination of two or more.

Among the above-mentioned silicon compounds, a tetraethoxysilaneoligomer, a mixture of a tetraethoxysilane oligomer and fine powderysilica, and the like are preferable from the standpoint of excellentuniformity and handling property.

The above-mentioned silicon compound preferably has high purity, and thecontent of each impurity at the initial period is preferably 20 ppm orless, more preferably 5 ppm or less.

As the above-mentioned organic compound generating carbon by heating, aliquid organic compound may be used alone and a liquid organic compoundand a solid organic compound may be used together.

As the above-mentioned organic compound generating carbon by heating,organic compounds manifesting high carbon-remaining ratio and beingpolymerized or crosslinked by a catalyst or heat are preferable, and forexample, monomers and prepolymers of phenol resins, furan resins, resinssuch as polyimides, polyurethanes, polyvinyl alcohol and the like, arepreferable, and additionally, liquid substances such as cellulose,sucrose, pitch, tar and the like are mentioned. Among them, those ofhigh purity are preferable, phenol resins are more preferable, and resoltype phenol resins are particularly preferable.

The above-mentioned organic compound generating carbon by heating may beused alone dr in combination of two or more.

The purity of the above-mentioned organic compound generating carbon byheating can be appropriately selected depending on the object, and whena high purity silicon carbide powder is necessary, it is preferable touse organic compounds in which the content of each metal is not 5 ppm ormore.

The above-mentioned polymerization catalyst and crosslinking catalystcan be appropriately selected depending on the above-mentioned organiccompound generating carbon by heating, and when the above-mentionedorganic compound generating carbon by heating is a phenol resin or furanresin, acids such as toluenesulfonic acid, toluenecarboxylic acid,acetic acid, oxalic acid, maleic acid, sulfuric acid and the like arepreferable, and maleic acid is particularly preferable.

The ratio of carbon contained in the above-mentioned organic compoundgenerating carbon by heating to silicon contained in the above-mentionedsilicon compound (hereinafter, abbreviated as C/Si ratio) is defined byelement-analyzing a carbide intermediate obtained by carbonizing amixture of them at 1000° C. Stoichiometrically, the content of freecarbon in a silicon carbide powder obtained when the above-mentionedC/Si ratio is 3.0 should be 0%, however, free carbon generates at lowerC/Si ratio by vaporization of a simultaneously produced SiO gas,actually. It is preferable to previously determine the compounding ratioso that the amount of free carbon in the resulted silicon carbide powderis suitable amount. Usually, by calcinations at 1600° C. or higher ataround 1 atm, free carbon can be controlled when the above-mentionedC/Si ratio is 2.0 to 2.5. When the above-mentioned C/Si ratio is over2.5, the above-mentioned free carbon increases remarkably. However, whencalcinations is conducted at lower atmosphere pressure or higheratmosphere pressure, the C/Si ratio for obtaining a pure silicon carbidepowder varies, therefore, the ratio is not necessarily limited in theabove-mentioned C/Si range, in this case.

The above-mentioned silicon carbide powder is obtained also by hardeninga mixture of the above-mentioned silicon compound and theabove-mentioned organic compound generating carbon by heating, forexample.

As the above-mentioned hardening method, a method of hardening byheating, a method of hardening by a hardening catalyst, methods usingelectronic beam and radiation, and the like are listed.

The above-mentioned hardening catalyst can be appropriately selecteddepending on the kind of the above-mentioned organic compound generatingcarbon by heating, and the like, and in the case of a phenol resin orfuran resin, acids such as toluenesulfonic acid, toluenecarboxylic acid,acetic acid, oxalic acid, hydrochloric acid, sulfuric acid, maleic acidand the like, amic acids such as hexamine, and the like are suitablylisted. When these hardening catalysts are used, the hardening catalystis dissolved or dispersed in a solvent. As the above-mentioned catalyst,lower alcohols (for example, ethyl alcohol and the like), ethyl ether,acetone and the like are listed.

A silicon carbide powder obtained as described above is calcinated in anon-oxidizing atmosphere such as nitrogen, argon and the like at 800 to1000° C. for 30 to 120 minutes.

By the above-mentioned calcinations, the above-mentioned silicon carbidepowder becomes a carbide, and by calcinating this carbide in anon-oxidizing atmosphere such as argon and the like at 1350 to 2000° C.,a silicon carbide powder is produced.

The temperature and time of the above-mentioned calcinations can beappropriately selected depending on the granular size of a siliconcarbide powder to be obtained, and the above-mentioned temperature ispreferably from 1600 to 1900° C. from the standpoint of more effectiveproduction of a silicon carbide powder.

For the purpose of removing impurities and obtaining a high puritysilicon carbide powder, after the above-mentioned calcinations, it ispreferable to conduct heat treatment at 2000 to 2400° C. for 3 to 8hours.

Since the silicon carbide powder obtained as described above hasnon-uniform size, given particle size can be obtained by powderdestruction, classification and the like.

The average particle size of the above-mentioned silicon carbide powderis preferably from 10 to 700 μm, more preferably from 100 to 400 μm.

When the above-mentioned average particle size is less than 10 μm,sintering occurs quickly at the sublimation temperature (1800 to 2700°C.) of silicon carbide for growing a silicon carbide single crystal,therefore, sublimation surface area decreases and growth of a siliconcarbide single crystal delays, in some cases, and when a silicon carbidepowder is accommodated in the above-mentioned reaction vessel and whenthe pressure of a re-crystallization atmosphere is changed for controlof the growth speed, a silicon carbide powder is splashed easily. On theother hand, when the above-mentioned average particle size is over 500μm, the specific surface area of a silicon carbide powder itselfdecreases, therefore, growth of a silicon carbide single crystal maydelay also in this case.

As the above-mentioned silicon carbide powder, any of 4H, 6H, 15R, 3Cand mixtures of them may be used. The grade of the above-mentioned 3Csilicon carbide powder is not particularly restricted, and thosegenerally marketed may be permissible, however, those of high purity arepreferable.

Further, nitrogen or aluminum and the like can be introduced into asilicon carbide single crystal grown using the above-mentioned siliconcarbide powder for the purpose of giving n type or p type conductivity,and when nitrogen or aluminum is introduced in generating theabove-mentioned silicon carbide powder, it is recommendable that, first,the above-mentioned silicon source, the above-mentioned carbon source,an organic substance composed of a nitrogen source or aluminum source,the above-mentioned polymerization catalyst or crosslinking catalyst areuniformly mixed. In this case, it is preferable that, for example, whena carbon source such as phenol resins and the like, an organic substancecomposed of a nitrogen source such as hexamethylenetetramine and thelike and a polymerization or crosslinking catalyst such as maleic acidand the like are dissolved in a solvent such as ethanol and the like,they are mixed sufficiently with a silicon source such as atetraethoxysilane oligomer and the like.

As the above-mentioned organic substance composed of a nitrogen source,substances generating nitrogen by heating are preferable, and listedare, for example, polymer compounds (specifically, polyimide resins,nylon resins and the like), various amines such as organic amines(specifically, hexamethylenetetramine, ammonia, triethylamine, and thelike, and compounds and salts of them). Of them, hexamethylenetetramineis preferable. A phenol resin synthesized using hexamine as a catalystand containing nitrogen derived from this synthesis process in an amountof 2.0 mmol or more based on 1 g of the resin can also be suitably usedas the organic substance composed of a nitrogen source. These organicsubstances composed of a nitrogen source may be used alone or incombination of two or more. The above-mentioned organic substancecomposed of an aluminum source is not particularly restricted and can beappropriately selected depending on the object.

Regarding the addition amount of the above-mentioned organic substancecomposed of a nitrogen source, when the above-mentioned silicon sourceand the above-mentioned carbon source are added simultaneously, nitrogenis contained in an amount of preferably 1 mmol or more based on 1 g ofthe above-mentioned silicon source, and the organic substance is addedin an amount of 80 to 1000 μg based on 1 g of the above-mentionedsilicon source.

—Sublimation—

It is preferable to conduct sublimation of the above-mentionedsublimation raw material by using a separate heating means from aheating means for effecting heating necessary for re-crystallization,from the standpoints of precise control and independent control of theheating means and prevention of interference and the like. In thisembodiment, the number of heating means is two or more, and two heatingmeans are preferably used in the present invention.

In the preferable embodiment in which two of the above-mentioned heatingmeans are used, a heating means for forming a sublimation atmosphereenabling sublimation of the above-mentioned sublimation raw material isa first heating means and a heating means for forming theabove-mentioned re-crystallization atmosphere enablingre-crystallization of the above-mentioned sublimation raw material beingsublimate only around the above-mentioned seed crystal of a siliconcarbide single crystal is a second heating means.

The above-mentioned first heating means is placed at the one end(sublimation raw material accommodating part) side of theabove-mentioned reaction vessel, forms a sublimation atmosphere so as toenable sublimation of the above-mentioned sublimation raw material, andheats the above-mentioned sublimation raw material to cause sublimation.

The above-mentioned first heating means is not particularly restrictedand can be appropriately selected depending on the object, and forexample, induction heating means, resistance heating means and the likeare listed, and the induction heating means are preferable sincetemperature control is easy, and among the induction heating means,induction-heatable coils are preferable.

When the above-mentioned first heating means is an induction-heatablecoil, the number of winding is not particularly restricted and can bedetermined so that heating efficiency and temperature efficiency areoptimum depending on the distance from the above-mentioned secondheating means, the material of the above-mentioned reaction vessel, andthe like.

—Growth of Silicon Carbide Single Crystal—

Growth of the above-mentioned silicon carbide single crystal isconducted on a seed crystal of a silicon carbide single crystal placedon the above-mentioned another end (seed crystal placing part) of theabove-mentioned reaction vessel.

Regarding the above-mentioned seed crystal of a silicon carbide singlecrystal, the polymorphs, size and the like of the crystal can beappropriately selected depending on the object, and as the polymorphs ofthe crystal, the same polymorph as that of a silicon carbide singlecrystal to be obtained is selected, usually.

For re-crystallizing and growing the above-mentioned silicon carbidesingle crystal on the above-mentioned seed crystal, it is preferable toform a re-crystallization atmosphere having temperature lower than thetemperature for sublimation of the above-mentioned sublimation rawmaterial and enabling re-crystallization of the above-mentionedsublimation raw material being sublimate only around the above-mentionedseed crystal (in other words, temperature distribution and atmosphere sothat temperature becomes lower when approximating the center part(center of the inside region), along the diameter direction of a surfaceon which the above-mentioned seed crystal is placed).

Formation of the above-mentioned re-crystallization atmosphere can bemore suitably conducted by the above-mentioned second heating means.Such a second heating means is placed at another end (seed crystalplacing part) side of the above-mentioned reaction vessel and forms are-crystallization atmosphere so as to enable re-crystallization of theabove-mentioned sublimation raw material being sublimate by theabove-mentioned first heating means only around the seed crystal of asilicon carbide single crystal, and causes re-crystallization of thesublimation raw material on the above-mentioned seed crystal of asilicon carbide single crystal.

The above-mentioned second heating means is not particularly restrictedand can be appropriately selected depending on the object. For example,induction heating means, resistance heating means and the like arelisted, and the induction heating means are preferable since temperaturecontrol is easy, and among the induction heating means,induction-heatable coils are preferable.

When the above-mentioned second heating means is an induction-heatablecoil, the number of winding is not particularly restricted and can bedetermined so that heating efficiency and temperature efficiency areoptimum depending on the distance from the above-mentioned first heatingmeans, the material of the above-mentioned reaction vessel, and thelike.

The quantity of induction heating current flowing through theabove-mentioned second heating means can be appropriately determineddepending on relation with the quantity of induction heating currentflowing through the above-mentioned first heating means, and regardingthe relation of them, it is preferable that the current value ofinduction heating current in the above-mentioned first heating means islarger than the current value of induction heating current in theabove-mentioned second heating means. This case is advantage in that thetemperature of a re-crystallization atmosphere around on theabove-mentioned seed crystal is maintained lower than the temperature ofan atmosphere in which the above-mentioned sublimation raw materialsublimates, and re-crystallization is conducted easily.

It is preferable to control the current value of induction heatingcurrent in the above-mentioned second heating means so that it decreasescontinuously or gradually when the diameter of a silicon carbide singlecrystal to be grown increases. In this case, the heating quantity by theabove-mentioned second heating means is controlled small when theabove-mentioned silicon carbide single crystal grows, consequently,re-crystallization is conducted only around the above-mentioned siliconcarbide single crystal keeping growing, and formation of polycrystalsaround the silicon carbide single crystal is effectively suppressed,advantageously.

A preferable tendency is obtained when the current value of inductionheating current in the above-mentioned second heating means iscontrolled small when the diameter of the above-mentioned seed crystalof a silicon carbide single crystal is large and controlled large whenthe above-mentioned diameter is small.

In the present invention, the above-mentioned second heating means canbe controlled independently from the above-mentioned first heatingmeans, therefore, preferable growth speed can be maintained through theall growth processes of a silicon carbide single crystal byappropriately controlling the heating quantity of the second heatingmeans depending on the growth speed of a silicon carbide single crystal.

The temperature of a re-crystallization atmosphere formed by theabove-mentioned second heating means is lower than the temperature ofthe above-mentioned sublimation atmosphere formed by the above-mentionedfirst heating means by preferably 30 to 300° C., more preferably 30 to150° C.

The pressure of a re-crystallization atmosphere formed by theabove-mentioned second heating means is preferably from 10 to 100 Torr(1330 to 13300 Pa). When this pressure condition is applied, it ispreferable that pressure reduction is not effected at ambienttemperature, and after heating to given temperature, pressure reductionis effected to control pressure condition so as to fall within theabove-mentioned given numerical value range.

It is preferable that the above-mentioned re-crystallization atmosphereis an inert gas atmosphere composed of an argon gas and the like.

In the present invention, it is preferable from the standpoint ofobtaining a silicon carbide single crystal having large diameter thattemperature at one end (sublimation raw material accommodating part)side accommodating a sublimation raw material, in the above-mentionedreaction vessel, controlled by the above-mentioned first heating means,temperature of the center part at another end (seed crystal placingpart) side carrying the above-mentioned seed of a silicon carbide singlecrystal placed, in the above-mentioned reaction vessel, controlled bythe above-mentioned second heating means, and temperature of partssituated at the outside of the center part and adjacent to the innerperipheral surface part of the reaction vessel are controlled in arelation described below. Namely, it is preferable to conduct control sothat, if the temperature at one end side accommodating a sublimation rawmaterial is represented by T₁, the temperature at another end side atwhich a seed crystal of a silicon carbide single crystal is placed isrepresented by T₂, and the temperature of parts adjacent to the innerperipheral surface part of the reaction vessel, at another end side, isrepresented by T₃, then, T₃-T₂ and T₁-T₂ increase continuously orgradually.

In this case, since T₁-T₂ increases continuously or gradually, even if asilicon carbide single crystal keeps on growing toward theabove-mentioned one end side with the lapse of time, the peak side ofcrystal growth of the silicon carbide single crystal is usuallymaintained at condition liable to cause re-crystallization. On the otherhand, since T₃-T₂ increases continuously or gradually, even if a siliconcarbide single crystal keeps on growing toward the outer peripheraldirection at above-mentioned another end side with the lapse of time,the outer peripheral end side of crystal growth of the silicon carbidesingle crystal is usually maintained at condition liable to causere-crystallization. As a result, production of a silicon carbide singlecrystal is effectively suppressed, and the silicon carbide singlecrystal keeps on growing toward the direction of increasing itsthickness while enlarging its diameter, finally, a silicon carbidesingle crystal having large diameter is obtained without contaminationof a silicon carbide polycrystal and the like, advantageously.

In the present invention, the above-mentioned silicon carbide singlecrystal re-crystallizes and grows according to the above-mentioned firstto third embodiments.

In the above-mentioned first embodiment, the above-mentioned siliconcarbide single crystal is allowed to grow while keeping the wholesurface of its growth surface in convex shape through the all growthprocesses. In this case, a concave portion sunk toward theabove-mentioned another end (seed crystal placing part) side is notshaped in the form of ring, at the whole surface of the growth surfaceof the silicon carbide single crystal.

In the above-mentioned second embodiment, growth of the above-mentionedsilicon carbide single crystal is conducted only in the region exceptingparts adjacent to the peripheral surface part in the reaction vessel(inside region), at the above-mentioned end of the above-mentionedreaction vessel. In this case, a silicon carbide polycrystal does notgrow contacting with the peripheral surface part in the reaction vessel,at the above-mentioned another end (seed crystal placing part).Therefore, when a silicon carbide single crystal grown is cooled to roomtemperature, stress based on a difference in thermal expansion does notconcentrate from the silicon carbide polycrystal side to the siliconcarbide single crystal side, and breakages such as cracking and the likedo not occur on the resulted silicon carbide single crystal.

In the above-mentioned third embodiment, the above-mentioned siliconcarbide single crystal is grown only at the region excepting partsadjacent to the peripheral surface part of in the reaction vessel(inside region), at the above-mentioned end of the above-mentionedreaction vessel, while keeping the whole surface of its growth surfacein convex shape through the all growth processes.

In this case, a concave portion sunk toward to the above-mentionedanother end (seed crystal placing part) side of the above-mentionedreaction vessel is not shaped in the form of ring at the whole surfaceof its growth surface of the above-mentioned silicon carbide singlecrystal, and a silicon carbide single crystal does not grow contactingwith the peripheral surface part in the reaction vessel, at theabove-mentioned another end (seed crystal placing part). Therefore, whena silicon carbide single crystal grown is cooled to room temperature,stress based on a difference in thermal expansion does not concentratefrom the silicon carbide polycrystal side to the silicon carbide singlecrystal side, and breakages such as cracking and the like do not occuron the resulted silicon carbide single crystal.

Regarding the form of the above-mentioned silicon carbide single crystalto be grown, it is preferable that the whole surface of its growthsurface is in convex form toward its growth direction side, and when theabove-mentioned one end (sublimation raw material accommodating part)faces the above-mentioned another end (seed crystal placing part), it ispreferable that the whole surface of its growth surface is in convexform toward the above-mentioned sublimation raw material side, namely,toward the above-mentioned one end (sublimation raw materialaccommodating part) side.

This case is preferable in that a concave portion sunk toward theabove-mentioned another end (seed crystal placing part) side is notpresent, on which contamination of polycrystals and polymorphs issignificant and concentration of stress based on a difference in thermalexpansion is believed to be easy.

Regarding the form of the above-mentioned silicon carbide single crystalto be grown, it may not in the above-mentioned convex form or a flatportion may be partially contained, providing the whole surface of itsgrowth surface does not contain a part sunk toward the reverse side toits growth direction side.

The form of a silicon carbide crystal containing a silicon carbidesingle crystal is preferably in angle form toward the above-mentionedsublimation raw material side, namely, toward the above-mentioned oneend side, and an approximate protruded shape having diameter decreasinggradually is more preferable. In other words, it is preferable that asilicon carbide crystal containing a silicon carbide single crystal isallowed to grow while keeping approximate protruded shape havingdiameter decreasing gradually when approximating the sublimation rawmaterial side, through the all growth processes.

In skirt parts of a silicon carbide crystal in the form of theabove-mentioned approximate protruded shape, namely, at outer peripheralparts, silicon carbide polycrystals and polymosphism may be mixed,however, generation of this mixing can be prevented by combination ofthe thickness, size, form and the like of the above-mentioned seedcrystal with the heating quantity by the above-mentioned second heatingmeans. Prevention of the contamination of silicon carbide polycrystalsand polymorphs is preferable since then the above-mentioned siliconcarbide crystal containing silicon carbide can be made only of a siliconcarbide single crystal.

In the present invention, a plate member in the form of ring may also befixed and placed on the peripheral surface part in the above-mentionedreaction vessel, approximately in parallel to the above-mentionedanother end (seed crystal placing part). In this case, when theabove-mentioned silicon carbide single crystal is re-crystallized andgrown on the above-mentioned seed crystal, only the above-mentionedsilicon carbide single crystal can be re-crystallized and grown on theabove-mentioned seed crystal, and a silicon carbide polycrystal is notallowed to grow or can be deposited selectively on the above-mentionedplate member in the form of ring. In this case, the diameter of theresulting silicon carbide single crystal is constrained corresponding tothe size of the above-mentioned plate member in the form of ring.

In the present invention, it is preferable, for the purpose of effectingefficient growth of the above-mentioned silicon carbide single crystal,to use an interference preventing means for preventing interferencebetween the above-mentioned first heating means and the above-mentionedsecond heating means.

The above-mentioned interference preventing means is not particularlyrestricted and can be appropriately selected depending on the kind ofthe above-mentioned first heating means and the above-mentioned secondheating means, and the like, and for example, interference preventingcoils, interference preventing plates and the like are listed, and whenthe above-mentioned first heating means and the above-mentioned secondheating means are the above-mentioned induction-heatable coil,interference preventing coils and the like are suitably listed.

The above-mentioned interference preventing coil (simply called as“coil” in some cases) is preferably a coil through which inductioncurrent flows and having a function of preventing interference betweenthe above-mentioned first heating means and the above-mentioned secondheating means by flowing induction current.

The above-mentioned interference preventing coil is preferably placedbetween the above-mentioned first heating means and the above-mentionedsecond heating means. This case is preferable in that, when inductionheating is conducted by the above-mentioned first heating means and theabove-mentioned second heating means simultaneously, induction currentflow through the interference preventing coil, and the interferencepreventing coil can minimize and prevent interference between them.

The above-mentioned interference preventing coil is preferably designedso that it is not heated by induction current flowing through itself, aself-coolable coil is more preferable, and a coil through which acooling medium such as water and the like can flow is particularlypreferable. This case is preferable in that, even if induction currentin the above-mentioned first heating means and the above-mentionedsecond heating means flows through the interference preventing coil, theinterference preventing coil is not heated, therefore, theabove-mentioned reaction vessel is also not heated.

The number of winding of the above-mentioned wound interferencepreventing coil is not particularly restricted and differs depending onthe kind of the above-mentioned first heating means and theabove-mentioned second heating means and the amount of current flowingthrough them, and the like and can not be limited to a constant range,namely, even a single coil is sufficient.

As described above, according to the method of producing a siliconcarbide single crystal of the present invention, the silicon carbidesingle crystal of the present invention having high quality can beeasily produced efficiently and in condition showing no breakages suchas cracking and the like.

(Silicon Carbide Single Crystal)

The silicon carbide single crystal of the present invention is producedby the method of producing a silicon carbide single crystal of thepresent invention described above.

In the silicon carbide single crystal of the present invention, thecrystal defects (pipe defect) of which image is optically detectednon-destructively is preferably 100/cm² or less, more preferably 50/cm²or less, particularly preferably 10/cm² or less.

The above-mentioned crystal defect can be detected, for example, by thefollowing manner. Namely, illumination prepared by adding suitableamount of transmission illumination to reflection illumination isallowed to irradiate the silicon carbide single crystal, and the focusof a microscope is adjusted to an opening of crystal defect (pipedefect) on the surface of the silicon carbide single crystal, then,portions continuing to the inside of the pipe defect can be observed asshadow weaker than an image of the opening, connected to the opening.Under such conditions, the whole surface of the silicon carbide singlecrystal is scanned to obtain a microscope image, then, this microscopeimage is image-treated, and only forms characteristic to the pipe defectare extracted and the number of them are counted. Thus, the pipe defectcan be detected.

According to the above-mentioned detection, only the above-mentionedpipe defect can be correctly detected, from a mixture of defects otherthan the above-mentioned pipe defect, such as extraneous substancesadhered to the surface of the above-mentioned silicon carbide singlecrystal, polishing flaw, void defect and the like, further, even finepipe defects of about 0.35 μm can be detected correctly. On the otherhand, there is conventionally conducted a method in which theabove-mentioned pipe defect parts are selectively etched, and detectedin magnification, however, this method has a problem that, adjacent pipedefects described above join mutually, and resultantly, smaller numberof defects than the real number of the pipe defects is detected.

The total content of the above-mentioned impurity elements in theabove-mentioned silicon carbide single crystal is preferably 10 ppm orless.

The silicon carbide single crystal of the present invention contains nocrystal defects such as contamination of polycrystals and polymorphs andmicropipes and the like and has extremely high quality: therefore, it isexcellent in dielectric breakdown property, heat resistance, radiationresistance and the like and particularly suitable for electronic devicessuch as semiconductor wafers and the like and optical devices such aslight emitting diodes and the like.

(Silicon Carbide Single Crystal Production Apparatus)

With the apparatus for generating a silicon carbide single crystal ofthe present invention, the above-mentioned sublimation raw materialbeing sublimate is re-crystallized to grow a silicon carbide singlecrystal, generating the silicon carbide single crystal of the presentinvention.

The above-mentioned apparatus for generating a silicon carbide singlecrystal comprises at least a crucible, a first induction heating coiland a second induction heating coil, and if necessary, other membersappropriately selected, and the like.

The above-mentioned crucible is not particularly restricted and can beappropriately selected from known products, and in general, comprises avessel body and a cover body.

The material of the above-mentioned crucible is not particularlyrestricted and can be appropriately selected from known materials, andgraphite is particularly preferable.

The above-mentioned vessel body is not particularly restricted providingit has a function capable of accommodating the above-mentionedsublimation raw material, and known products can be adopted.

The above-mentioned cover body is preferably attachable to anddetachable from the above-mentioned vessel body, and known products canbe adopted. The above-mentioned vessel body and the above-mentionedcover body may be designed so that attachable and detachable by any ofengagement, spiral fitting and the like, and spiral fitting ispreferable.

In the above-mentioned apparatus for generating a silicon carbide singlecrystal, usually, when the above-mentioned cover body is installed tothe above-mentioned vessel body, a seed crystal of the above-mentionedsilicon carbide single crystal is placed at approximately the center ofa surface facing the above-mentioned sublimation raw materialaccommodated in the vessel body.

The above-mentioned first induction heating coil is not particularlyrestricted providing it generates heat by flow of current and can form asublimation atmosphere so as to enable sublimation of theabove-mentioned sublimation raw material, and induction heatable coilsand the like are suitably listed.

The above-mentioned first induction heating coil is placed in conditionwound around the outer periphery of a part accommodating theabove-mentioned sublimation raw material, in the above-mentionedcrucible.

The above-mentioned second induction heating coil is not particularlyrestricted providing it can form a re-crystallization atmosphere so thatthe above-mentioned sublimation raw material being sublimate by theabove-mentioned first induction heating coil can re-crystallize onlyaround the above-mentioned seed crystal of silicon carbide, tore-crystallize the sublimation raw material on the above-mentioned seedcrystal of silicon carbide, and induction-heatable coils and the likeare listed.

The above-mentioned second induction heating coil is placed in conditionwound around the outer periphery of a part on which the above-mentionedseed crystal of silicon carbide is placed, in the above-mentionedcrucible.

In the above-mentioned silicon carbide single crystal productionapparatus, the above-mentioned first induction heating coil forms asublimation atmosphere so as to enable sublimation of theabove-mentioned sublimation raw material, to sublimate theabove-mentioned sublimation raw material. The above-mentioned secondinduction heating coil forms a re-crystallization atmosphere so that theabove-mentioned sublimation raw material being sublimate by theabove-mentioned first induction heating coil can be re-crystallized onlyaround the above-mentioned seed crystal, to re-crystallize thesublimation raw material on the above-mentioned seed crystal. Therefore,the whole surface of its growth surface of a silicon carbide singlecrystal to be grown is maintained in convex form toward its growthdirection in the all growth processes, a concave portion sunk toward theabove-mentioned cover body is not shaped in the form of ring, andsilicon carbide polycrystal does not grow contacting the peripheralsurface part in the above-mentioned vessel body. Therefore, when asilicon carbide single crystal grown is cooled to room temperature,stress based on a difference in thermal expansion does not concentratefrom the silicon carbide polycrystal side to the silicon carbide singlecrystal side, and breakages such as cracking and the like do not occuron the resulted silicon carbide single crystal. As a result, a highquality silicon carbide single crystal can be efficiently and securelyproduced having no conventional various problems described above,namely, having no breakages such as cracking and the like and crystaldefects such as contamination of polycrystals and polymorphs andmicropipes and the like present.

As described above, according to the silicon carbide single crystalproduction apparatus for the present invention, the silicon carbidesingle crystal of the present invention having high quality can beproduced efficiently and easily without breakages such as cracking andthe like.

EXAMPLES

The following examples will described the present invention, but do notlimit the scope of the invention at all.

Example 1

Using a silicon carbide single crystal production apparatus 1 shown inFIG. 1, a silicon carbide single crystal was produced. Use of thesilicon carbide single crystal production apparatus 1 leads to executionof the silicon carbide single crystal production method of the presentinvention.

The silicon carbide single crystal production apparatus 1 comprises agraphite crucible 10 having a vessel body 12 capable of accommodating asublimation raw material 40 and a cover body 11 which can be attached toand detached from the vessel body 12 by spiral fitting, and in which,when installed on the vessel body 12, a seed crystal 50 of a siliconcarbide single crystal can be placed approximately at the center of asurface facing the sublimation raw material 40 accommodated in thevessel body 12; a supporting rod 31 fixing the graphite crucible 10 toinside of a quartz tube 30; a first induction heating coil 21 placed ata part which is on the outer periphery of the quartz tube and in whichthe sublimation raw material 40 is accommodated, in the graphitecrucible 10; and a second induction heating coil 20 placed at a partwhich is on the outer periphery of the quartz tube 30 and on which thecover body 11 is situated, in the graphite crucible 10. The graphitecrucible 10 is covered with an insulation material (not shown).

The sublimation raw material 40 is a silicon carbide powder (6H(partially containing 3C), average particle size: 200 μm) obtained byusing a high purity tetraethoxysilane polymer described above as asilicon source, a resol type phenol resin as a carbon source, and mixingthem uniformly to obtain a mixture, calcinating the mixture by heatingunder an argon atmosphere, and the seed crystal 50 of a silicon carbidesingle crystal is a Rayleigh crystal of 6H.

In the silicon carbide single crystal production apparatus 1, electriccurrent was allowed to flow through the first induction heating coil 21.By this heat, the sublimation raw material 40 was heated (after heatingto 2500° C., pressure was maintained at 50 Torr (6645 Pa) by an argongas atmosphere). The sublimation raw material 40 was heated up to giventemperature (2500° C.) to show sublimation: The sublimation raw material40 sublimated does not re-crystallize unless cooled to there-crystallization temperature. Here, the cover body 11 side was heatedby the second induction heating coil 20 and had temperature lower thanthe sublimation raw material 40 side (temperature of seed crystal is2400° C.), and maintained in a re-crystallization atmosphere (pressureis 50 Torr (6645 Pa)) in which the sublimation raw material 40sublimated can re-crystallize, therefore, silicon carbidere-crystallized only around on the seed crystal 50 of a silicon carbidesingle crystal, and a crystal of silicon carbide grew.

Here, a silicon carbide single crystal 60 re-crystallizes and grows onthe seed crystal 50 of a silicon carbide single crystal, and a siliconcarbide polycrystal 70 re-crystallizes and grows on the outer peripheryon the seed crystal 50 of a silicon carbide single crystal, as shown inFIG. 2. In growth of the silicon carbide single crystal 60, a convexform was maintained toward the sublimation raw material 40 side in theall growth processes, and a concave portion sunk toward the cover body11 side was no shaped in the form of ring, and the silicon carbidesingle crystal 70 did not grow contacting the peripheral surface part 13in the vessel body 12.

As a result, when the silicon carbide single crystal 60 grown was cooledto room temperature, stress based on a difference in thermal expansionwas no applied in concentration from the silicon carbide polycrystal 70side to the silicon carbide single crystal 60 side, and breakages suchas cracking and the like did not occur on the resulted silicon carbidesingle crystal 60, as shown in FIG. 3.

When the resulted silicon carbide single crystal 60 was evaluated,contamination of polycrystals and polymorphs crystals was not found, andcrystal defect of micropipes was as scarce as 4/cm², meaning extremelyhigh quality.

The above-mentioned crystal defect of micropipes was detected asdescribed below, after cutting the resulted silicon carbide singlecrystal 60 into a thickness of 0.4 mm, mirror polishing to give a waferhaving a surface roughness of 0.4 nm, and removing extraneous substanceson the surface as much as possible by alkali washing. Namely,illumination prepared by adding suitable amount of transmissionillumination to reflection illumination was allowed to irradiate theabove-mentioned wafer after alkali washing, the focus of a microscopewas adjusted to an opening of micropipes on the wafer surface, then,portions continuing to the inside of the micropipe could be observed asshadow weaker than an image of the opening, connected to the opening.Under such conditions, the whole surface of the above-mentioned waferwas scanned to obtain a microscope image, then, this microscope imagewas image-treated, and only forms characteristic to the micropipe areextracted and the number of them were counted. Thus, the micropipes weredetected. In this detection, even fine micropipes of about 0.35 μm weredetected correctly without breakage.

Example 2

The same procedure as in Example 1 was conducted except that thegraphite crucible 10 was changed to a graphite crucible 10 shown in FIG.4 in Example 1. As a result, the same result as in Example 1 wasobtained. The graphite crucible 10 shown in FIG. 4 differs from thegraphite crucible 10 shown in FIG. 1 used in Example 1 only in that aninside region forming part 15 is provided in the cover body 11. Theinside region forming part 15 is, as shown in FIG. 4, a cylinder havingthe above-mentioned inside region on which a seed crystal of a siliconcarbide single crystal is placed as the bottom surface, and one end ofwhich is exposed to outside of the graphite crucible 10. The material ofinside region forming part 15 had a heat conductivity of 117 J/m/s/° C.(W/m·K), and the material of the cover body 11 other than inside regionforming part 15 had a heat conductivity of 129 J/m/s/° C. (W/m·K).

In the case of Example 2, since the above-mentioned inside region isformed of a different member (inside region forming part 15) from thatin the above-mentioned outside region, heating is difficult by adifference in contact resistance, and one end of the inside regionforming part 15 is exposed to outside, heat is discharged to outsideeasily, therefore, re-crystallization of silicon carbide was conductedeasily.

Example 3

The same procedure as in Example 1 was conducted except that thegraphite crucible 10 was changed to a graphite crucible 10 shown in FIG.5 in Example 1. As a result, the same result as in Example 1 wasobtained. The graphite crucible 10 shown in FIG. 5 differs from thegraphite crucible 10 shown in FIG. 1 used in Example 1 only in that aninside region forming part 15 is provided in the cover body 11. Theinside region forming part 15 has, as shown in FIG. 5, a form having theabove-mentioned inside region on which a seed crystal of a siliconcarbide single crystal is placed as the bottom surface, of whichdiameter increases discontinuously in two stages toward theabove-mentioned outside, and one end of which is exposed to outside. Thematerial of inside region forming part 15 had a heat conductivity of 117J/m/s/° C. (W/m·K), and the material of the cover body 11 other thaninside region forming part 15 had a heat conductivity of 129 J/m/s/° C.(W/m·K).

In the case of Example 3 since the above-mentioned inside region isformed of a different member from that in the above-mentioned outsideregion, heating is difficult by a difference in contact resistance, andone end of the inside region forming part 15 is exposed to outside, heatis discharged to outside easily, therefore, re-crystallization ofsilicon carbide was conducted easily.

Example 4

The same procedure as in Example 1 was conducted except the followingpoint in Example 1. Namely, the resulted silicon carbide powder had 6Hand an average particle size of 300 μm, and the seed crystal 50 of asilicon carbide single crystal is a 15R wafer (diameter: 40 mm,thickness 0.5 mm) obtained by cutting the bulk silicon carbide singlecrystal obtained in Example 1 and mirror-polishing the whole surface.

Current of 20 kHz was flown through a first induction heating coil 21 toheat, and current of 40 kHz was flown through a second induction heatingcoil 20 to heat to increase the temperature. The lower part of thegraphite crucible 10 (part accommodating the sublimation raw material40) was heated to 2312° C., and the upper part of the graphite crucible10 (place on which the seed crystal 50 of a silicon carbide singlecrystal is placed in the cover body 11) was heated to 2290° C.,respectively. In this operation, the feeding powder to the firstinduction heating coil 21 was 10.3 kW, and the induction heating current(feeding current to LC circuit) was 260 A, and the feeding power to thesecond induction heating coil 20 was 4.6 kW, and the induction heatingcurrent was 98 A. The pressure was reduced to 20 Torr (2658 Pa) fromnormal pressure over 1 hour, and maintained for 20 hours, to obtain asilicon carbide single crystal 60 of which convex form was maintainedtoward the sublimation raw material 40 side as shown in FIG. 6. In thissituation, the height to the peak of the convex form in the siliconcarbide single crystal 60 was 12 mm, and the diameter of a grown crystalof silicon carbide containing the silicon carbide single crystal 60 anda silicon carbide polycrystal formed around this was 87 mm. In thesilicon carbide single crystal 60, a concave portion sunk toward thecover body 11 was not shaped in the form of ring. The silicon carbidesingle crystal 60 did not grow contacting the peripheral surface part 13of the vessel body 12 of the graphite crucible 10. Further, a siliconcarbide single crystal 70 generated only slightly around the siliconcarbide single crystal 60.

Example 5

The same procedure as in Example 1 was conducted except the followingpoint in Example 4. Namely, the procedure was as in Example 4 exceptthat the seed crystal 50 of a silicon carbide single crystal had adiameter of 20 mm and a thickness of 0.5 mm, the lower part of thegraphite crucible 10 (part accommodating the sublimation raw material40) was heated to 2349° C., and heating temperature of the upper part ofthe graphite crucible 10 (place on which the seed crystal 50 of asilicon carbide single crystal is placed in the cover body 11) was 2317°C., and under these conditions, the feeding powder to the secondinduction heating coil 20 was 5.5 kW, the induction heating current was118 A, and the diameter of a grown crystal of silicon carbide containingthe silicon carbide single crystal 60 and a silicon carbide polycrystalformed around this was 60 mm, and the same excellent results wereobtained as in Example 4.

Example 6

The same procedure as in Example 1 was conducted except the followingpoint in Example 6. Namely, an interference preventing coil 22 was usedin which water flows and which can be cooled. The resulted siliconcarbide powder had 6H and an average particle size of 250 μm, and theseed crystal 50 of a silicon carbide single crystal is a wafer (6H)having a diameter of 25 mm and a thickness of 2 mm obtained by cuttingthe bulk silicon carbide single crystal obtained in Example 4 andmirror-polishing the whole surface.

Current of 20 kHz was flown through a first induction heating coil 21 toheat, and current of 40 kHz was flown through a second induction heatingcoil 20 to heat. The lower part of the graphite crucible 10 (partaccommodating the sublimation raw material 40) and the upper part of thegraphite crucible 10 (place on which the seed crystal 50 of a siliconcarbide single crystal is placed in the cover body 11) were heated to2510° C., respectively, and heated for 1 hour. While maintaining thelower part of the graphite crucible 10 at the same temperature (T₁), thefeeding power to the second induction heating coil 20 was graduallylowered (from 5.8 kW, 120 A, to 4.2 kW, 90 A), to lower the temperatureof the seed crystal placing part of the cover body 11 of the graphitecrucible 10 down to 2350° C. (T₂) over 20 hours and to lower thetemperature of the outer peripheral part of the seed crystal placingpart of the cover body 11 down to a calculated estimated temperature of2480° C. (T₃), respectively. In this operation, the pressure wasdecreased simultaneously from normal pressure to 20 Torr (2658 Pa) over1 hour, as a result, a silicon carbide single crystal 60 of which convexportion was maintained toward the sublimation raw material 40 side wasobtained, as shown in FIG. 7. In this situation, the height to the peakof the convex form in the silicon carbide single crystal 60 was 18 mm.In the silicon carbide single crystal 60, a concave portion sunk towardthe cover body 11 was not shaped in the form of ring. The siliconcarbide single crystal 60 did not grow contacting the peripheral surfacepart 13 of the vessel body 12 of the graphite crucible 10. Further, asilicon carbide single crystal 70 did not generate or grow adjacent toand around the silicon carbide single crystal 60.

Example 7

The same procedure as in Example 1 was conducted except the followingpoint in Example 1. Namely, the second induction heating coil 20 and thefirst induction heating coil 21 were substituted by an induction heatingcoil 25 in a conventional silicon carbide single crystal productionapparatus 80 shown in FIG. 8, and only on outside regions of a circlehaving a radius of 60 mm from the center, of surfaces (surfaces on whichgrowth of silicon carbide single crystal is conducted) facing the insideof the vessel body 12, on the cover body 11 of the graphite crucible, acarbon thin membrane which is judged to be glassy or amorphous by X raydiffraction was formed by the following method to give a thickness of 1to 10 μm. Its was placed in a vacuum chamber while exposing only theabove-mentioned outside regions on the cover body 11, and under abenzene atmosphere, the pressure in the chamber was controlled to 0.23Pa. Then, the cover body 11 was kept at a negative potential of 2.5 kV,and by decomposing benzene by ark discharge plasma generated at a facingpart of a filament ard an anode, positive ions generated in plasma wereallowed to collide against the above-mentioned outer regions on thecover body 11 at high speed, to effect membrane formation.

In Example 7, a crystal of silicon carbide did not grow on a part onwhich membrane formation of glassy carbon or amorphous carbon waseffected, on a surface of the side facing to the inside of the vesselbody 12 in the cover body 11, and only on the center part (circular parthaving a diameter of 60 mm) on which membrane formation was noteffected, a silicon carbide single crystal 60 grew of which wholesurface of its growth surface was maintained in convex form toward thesublimation raw material 40 side. Therefore, the silicon carbide singlecrystal 60 did not grow contacting the peripheral surface part 13 of thevessel body 12 in the graphite crucible 10, and when cooled to roomtemperature, breakages such as cracking and the like did not occur.

Comparative Example 1

A silicon carbide single crystal was produced in the same manner as inExample 1 except that a silicon carbide single crystal productionapparatus 80 shown in FIG. 6 was used.

Specifically, the same procedure was conducted as in Example 1 exceptthat the first induction heating coil 21 and the second inductionheating coil 20 placed at a pat which is situated at the outer peripheryof the quartz tube 30 and on which the cover body 11 in the graphitecrucible 10 is situated were substituted by induction heating coils 25placed under condition wound in spiral form at approximately the sameinterval at a part which is situated at the outer periphery of thequartz tube 30 and on which the graphite crucible 10 is situated, andthe interference preventing coil 22 was not used.

In Comparative Example 1, the whole surface of the side facing theinside of the vessel body 12, in the cover body 11, was, covered with acrystal of silicon carbide, and a silicon carbide single crystal 70 grewon the outer periphery of the cover body 11 contacting the innerperipheral surface of the vessel body 12, as shown in FIG. 8. Whencooling was conducted to room temperature under this condition, stressbased on a difference in thermal expansion is applied in concentrationfrom the silicon carbide polycrystal 70 side to the silicon carbidesingle crystal 60 side, and defects such as cracking and the likeoccurred on the silicon carbide single crystal 60, as shown in FIG. 8.

It will be understood by those skilled in the art that the examplesdescribed above are preferable embodiments of the present invention, anda lot of variations and modifications can be carried out withoutviolating the spirit and range of this invention.

According to the present invention, a high quality silicon carbidesingle crystal excellent in dielectric breakdown property, heatresistance, radiation resistance and the like, particularly suitably forelectronic devices such as semiconductor wafers and the like and opticaldevices such as light emitting diodes and the like, and showing nodefects such as contamination of polycrystals and polymorphs andmicropipes and the like, and a method and an apparatus capable ofgenerating the above-mentioned high quality silicon carbide singlecrystal with large diameter efficiently and easily without breakagessuch as cracking and the like, can be provided.

1-30. (canceled)
 31. An apparatus for generating a silicon carbidesingle crystal in which a sublimation raw material being sublimated isre-crystallized to grow a silicon carbide single crystal, comprising: acrucible provided with a vessel body to accommodate a sublimation rawmaterial and a cover body attachable to and detachable from the vesselbody and, when the cover body is installed on the vessel body and, whenthe cover body is installed on the vessel body, a seed crystal of asilicon carbide single crystal can be arranged at a surface facing theinside of the vessel body; a first induction heating coil wound aroundthe outer periphery of a part or the crucible when the sublimation rawmaterial is accommodated, so as to form a sublimation atmosphere toenable sublimation of the sublimation raw material; a second inductionheating coil wound around the outer periphery of a part of a cruciblewhere the seed crystal is placed, so as to form a re-crystallizationatmosphere so that the sublimation raw material being sublimate by thefirst induction heating coil is re-crystallize only in the vicinity ofthe seed crystal of a silicon carbide single crystal, andre-crystallizing the sublimation raw material on the seed crystal of asilicon carbide single crystal; and an interference preventing coli forproviding the induction current and preventing Interference between thefirst heating coil and the second heating oil, placed between the firstheating coil and the second heating oil.
 32. The apparatus of claim 1,wherein the interference preventing coil is a coil through which coolingwater can flow.
 33. The apparatus of claim 1, wherein the crucibleincludes a lower end and an upper end.
 34. The apparatus of claim 1,further comprising a quartz tube wherein the vessel is placed in thequartz tube.
 35. The apparatus of claim 1, wherein an induction currentflows through the Interference preventing coil, and the Interferencepreventing coil minimizes and prevents Interference between the firstheating coil and the second heating coil, when an Induction heating isconducted by the first heating coil and the second heating coilsimultaneously.